The present invention relates to resistive heaters, and particularly to heaters for use in smoking articles in which a tobacco flavor-generating medium is heated to release tobacco flavors.
Previously known smoking articles deliver flavor and aroma to the smoker as a result of tobacco combustion. During combustion, which typically occurs at temperatures in excess of 800.degree. C., various distillation and pyrolysis products are produced. As these products are drawn through the body of the smoking article toward the mouth of the smoker, they cool and condense to form an aerosol or vapor which provides the flavor and aroma associated with smoking.
Such conventional smoking articles have various perceived drawbacks associated with them, such as the production of sidestream smoke. Additionally, the combustion process cannot be easily suspended by the smoker in order to allow storage of the smoking article for later consumption. Although a conventional smoking article, such as a cigarette, may be extinguished prior to its being smoked to completion, it is typically not convenient or practical to save the cigarette for later use.
Alternative smoking articles are known where a flavor-generating medium of tobacco or a tobacco-derivative may be heated, without combustion, thereby releasing tobacco flavors without producing smoke. Smoking articles that provide a flavor aerosol without tobacco combustion are described in commonly assigned U.S. Pat. No. 5,146,934, and commonly assigned U.S. patent applications Ser. No. 07/443,636, filed Nov. 29, 1989 (Case PM-1389), and Ser. No. 07/732,619, filed Jul. 19, 1991 (PM-1353). Smoking articles may also use electrically-powered heaters to heat the tobacco flavor-generating medium. This generally requires that the tobacco medium be heated to a temperature of at least 300.degree. C., preferably within a period of 2.0 seconds and more desirably to a temperature above 500.degree. C. in less than 1 second.
Resistive heating elements for electric heaters may be constructed from ceramics. However, conventional ceramic heaters typically require a period of minutes to heat up. Further, a smoker of an electrically-powered smoking article should be able to either energize or shut off the article on demand. For use in electrically-powered smoking article, a resistive heater should also be small, and operate on low voltage batteries.
It would therefore be desirable to be able to provide a resistive heater for use in an electrically-powered smoking article.
It would also be desirable to be able to provide a low-voltage battery-powered ceramic heater that produces temperatures sufficiently high to release tobacco flavors from tobacco on a tobacco derivative.
It would further be desirable to be able to provide a ceramic heater that has a plurality of discrete resistive heating elements that may be individually energized.
It would still further be desirable to be able to provide a heater having ceramic heating elements that may be energized rapidly.
It would yet further be desirable to be able to provide a process for fabricating such a heater.